Antimalarial treatment and malaria transmission: insights from the field

Antimalarial treatment and malaria transmission:insights from the field

Abdoulaye DJIMDE PharmD, PhD

Malaria Research and Training Center

University of Bamako, Mali

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Atelier PaludismeInstitut Pasteur Antananarivo

14 – 20 Mars 2011

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• Drug Resistance

• Spread of drug resistance

Molecular Biology

Genetics

PK

Pharmacogenomics

Immunology

Policy

Host-Parasite-Vector

Transmission

Outline

1. Sulfadoxine-Pyrimethamine (SP) and malaria transmission in the field

2. Impact of SP on P. falciparumgametocytes infectivity in vitro

3. Artemisinin-based combinations and malaria transmission in sub-Saharan Africa

Conclusion3

P. falciparum life cycle

Current malaria control tools

• Artemisinin-based combination therapies (ACTs)

• Sulfadoxine-pyrimethamine recommended for IPT in pregnant women– contemplated for IPTi and IPTc

• Quinine for severe malaria

• Insecticide treated nets & indoor residual spray

Sulfadoxine-Pyrimethamine treatment and malaria transmission in a setting of

high Sulfadoxine-Pyrimethamine efficacy of Mali

Background

• Chloroquine efficacy decreasing

• Need alternative second line drug

• Prospective in vivo tests of CQ, amodiaquine and SP

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Study site

• Kolle: rural village; 2,500 people

• 55 Km South of Bamako

• P. falciparum malaria endemic and seasonal

• Parasitemia:

– 40-50% dry season (October-April)

– 70-85% rainy season (May-September). Kolle

Study design

• Open randomized drug efficacy trial

• Children 6 months – 5 years

• Three arms: Chloroquine, Amodiaquine, SP

• 28 days of follow up

• In vivo, in vitro , molecular and pharmacokinetic studies

MIM Antimalarial Drug Resistance Network

In vivo SP resistance in Mali

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Evolution of gametocyte carriage after SP treatment

Beavogui et al., IJP 2010

Molecular markers of SP resistance

Adapted from P. Wang et al. :Molecular and Biochemical Parasitology 89 (1997) 161–177

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Mutations in pre-treatment asexual vs. post-treatment gametocytes

0102030405060708090

100

%

DHFR108

DHFR59DHFR51DHPS43

7FRTrip

leQua

drup

le

AsexualGameto

*

**

* * p<0.001*

*

Beavogui et al., IJP 2010

Impact of large scale use of SP on spread of drug resistance and

malaria transmission?

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Methods

• Drug efficacy study• Screening for gametocyte carriers • Detect molecular markers of drug resistance• Include gametocyte carriers aged 6 – 18 y.• Direct feed starved F1 generation An. gambiae• Maintain mosquitoes in lab for 8 days• Presence and number of oocysts measured by

dissection• Compare the infectivity of pre-treatment vs. post-SP

gametocytes to Anopheles gambiae• Protocol approved by IRBs in Bamako & Maryland

16

17

Direct feeding

18

19

Infectivity of Post-treatment Gametocytes

* P < 0.001

Beavogui et al., IJP 2010

Summary 1

• SP increase rate of gametocyte carriage

• Post-SP gametocytes carry SP- resistance mutations

• Post-SP gametocytes were lesstransmissible to Anopheles gambiae

Mechanism of decreased infectivity of post-sulfadoxine-pyrimethamine P. falciparum

gametocytes to anophelinemosquitoes

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Infectivity of Sulfadoxine-Pyrimethamine treated P. FalciparumGametocytes to Anopheline Mosquitoes

Candle Jar Shaker Tipper

• Serum supplemented RPMI complete culture media

• Gas (O2, CO2 and Nitrogen) humidity (70 - 80%)

Gametocyte production

Gametocytes followup

Stage II

Day 8

Stage V

Day 14

Exflagellation test

Day 14

Standard Membrane feeding Assay

Feeding of 30 mosquitoes

With each sample

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Sulfadoxine and Pyrimethamine Plasma concentrations in Mali

S

P

Drugs Mean conc. Day 3 Day 7 Day 14

Sulfa -------

Pyr

ug/ml------------ng/ml

61-----------

158

34------------

67

14---------

16

Drug concentrations used

Experimental design

28A = Gametocytogenesis, B = Gametocyte maturation, C = Mature gametocyte infectivity Kone A, IJP, 2010

Results

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A. Induction of gametocytogenesis

30NF 135 Stage II NF135 Stage V

B. NF 135 Gametocyte development

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Controls Pyrimethamine- treated Sulfadoxine- treated

Kone A, IJP, 2010

C. Effect of S, P and SP on gameto infectivity

32Kone A, IJP, 2010

Effect of S, P and SP on oocyst density

33Kone A, IJP, 2010

Effect of Day3 levels of S or SP on mosquito survival

34Kone A, IJP, 2010

Summary 2

• Sulfadoxine and pyrimethamine have complex effects on the biology of gametocytogenesis.

• Induce differentiation into sexual forms

• Treatment of young gametocytes impaired their further development into mature stage V gametocytes.

• Drug + mature gametocytes => decreased infectivity

• SP also kills vector A. stephensi35

Artemisinine-based combination therapies and Malaria transmission

in the field

ACTs and malaria transmission

• “A single intramuscular injection of 5 mg/kg artemisinin (to gametocytemic rhesus monkeys) resulted in complete loss of mosquito infectivity within 24 h of drug administration” Dutta GP, et al. 1989

• “artemisinin derivatives reduced gametocyte carriage 18.5 fold”and “were found to reduce the transmission potential of falciparum malaria”Price RN et al.,1996

• “Artemesinin-based combination therapies (ACT) for falciparum malaria reduce gametocyte carriage, and therefore reduce transmission”.

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ACTs and malaria transmission (2)

• NASBA study in Kenya “data suggest that the potential of malaria transmission remains high even after treatment with artemisinin combination therapy”Schneider P. et al, IJP, 2006

• “An efficacious antimalarial regimen with no specific gametocytocidal properties but a long prophylactic time was estimated to be more effective at reducing transmission than a short-acting ACT in the highest-transmission setting”. Okell LC, PLoS Med, 2008

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Objective

Measure the impact of AS/AQ, AS/SP and AR-L on malaria transmission.

Day 28 Efficacynon-Corrected vs. PCR Corrected

** P < 0.05

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Evolution of gametocyte carriage by treatment arm on follow up days

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How infectious are the post-ACT gametocytes?

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Methods• Drug efficacy study• Screening for gametocyte carriers • Detect molecular markers of drug resistance• Include gametocyte carriers aged 6 – 18 y.• Direct feed starved F1 generation An. gambiae• Maintain mosquitoes in lab for 8 days• Presence and number of oocysts measured by dissection

• Compare the infectivity of pre-treatment vs. post-SP gametocytes to Anopheles gambiae

• Protocol approved by Ethics Committee of FMPOS

Study site

• Bougoula-Hameau: peri-urban village; 5000 people

~400 Km South of Bamako

• P. falciparum malaria hyper endemic

• No Insectaries around!!

Bougoula-Hameau, Sikasso, Mali

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46

47

48

49

Direct feeding

50

51

Comparing Ctrl vs. all post-ttt Oocyst positive

05

1015202530354045

Ctrl

ASSP

ASAQ

ARL

Treatment arms

Oocyst +

***

***

NS

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Summary 3

• ACTs decreased gametocyte carriage

HOWEVER

• Would all ACTs reduce malaria transmission in high transmission settings?

Discussion

• “Overall, infectivity was about three-times higher for direct feeding than for membrane feeding (p < 0.001)”Diallo M., et al Malaria Journal 2008

• MFA “Blood cells were separated from plasma by centrifugation and plasma was replaced by a similar volume of normal human plasma known to sustain malaria transmission. This step was performed to avoid the possible interference (blocking or enhancing) antibodies to gametocytes in the donor’s plasma”.

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Conclusions

• Malaria eradication/elimination will require new, safe and truely gametocytocidal drug

• Need more sensitive gametocyte assays that could indicate gametocyte viability in addition to prevalence and density.

• Field oriented studies need to be as close as possible to natural conditions. Too much cleaning of experimental design may yield nice results but with little relevance to real life. 54

Acknowledgements• MRTC

• Study sites & participants

• Pr. Doumbo O &

MRTC staff

• Nijmegen

• Adrian Luty

• Robert Sauerwein

• Support

• Government of Mali

• MIM/TDR

• NIAID/NIH

• FIC/NIH

• Ministère Français de la Recherche (Pal +)

• Sanofi-Aventis

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